A coated type magnetic recording medium which is prepared by dispersing magnetic particles or ferromagnetic metal particles such as .gamma.-Fe.sub.2 O.sub.3, Co-doped .gamma.-Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4, Co-doped .gamma.-Fe.sub.3 O.sub.4, CrO.sub.2, or a Bertholide compound of Fe.sub.3 O.sub.4 in an organic binder such as a copolymer of vinyl chloride and vinyl acetate, a copolymer of styrene and butadiene, an epoxy resin or a polyurethane resin, coating the resulting coating composition on a non-magnetic support and drying it has widely been used. With the recent increased demand for high density recording, a thin metal film type magnetic recording medium, of which a ferromagnetic thin metal film as a magnetic recording layer is prepared by a vapor-deposition method such as vacuum evaporation, sputtering, or an ion plating or metal plating method such as an electroplating method, or a non-electroless plating method without using a binder has drawn attention and has been developed to put into practice.
In order to realize a magnetic recording medium for high density recording, it is desirable theoretically and experimentally to have high coercive force and to make the medium thinner and thinner. In this connection, a thin metal film type magnetic recording medium is highly desirable, because their thickness is 1/10 less than thickness of the conventional coated tpe magnetic recording medium and saturation magnetic flux density is high.
Particularly, a vacuum evaporation method is very advantageous, because a step for disposing of a waste solution, as is required in a plating method, is unnecessary, the manufacturing process is simple and the speed for precipitating a film is high. As a method for vacuum evaporating a magnetic film having a desirable coercive force and squareness ratio on a magnetic recording medium, an oblique incident evaporation method is disclosed in U.S. Pat. Nos. 3,342,632 and 3,342,633.
However, the ferromagnetic thin metal film type magnetic recording medium has had problems, such as weather resistance, running properties, and wear resistance. Upon recording, reproducing, and erasing magnetic recording on a magnetic recording medium, the medium moves relatively to a magnetic head. On this occasion, the magnetic recording medium must run smoothly and stably without causing contacting, wearing, or damaging the magnetic head. Under these circumstances, it is examined and proposed to provide a lubricating layer or a protective layer in order to improve running properties and durability.
It is disclosed, for example, in Japanese Patent Application (OPI) Nos. 69824/85 and 85427/85 (the term "OPI" as used herein means an "unexamined published application") that a protective layer for a thin metal film type magnetic recording medium is prepared by dissolving thermoplastic resins, thermosetting resins, fatty acids, metal salts of fatty acids, fatty acid esters, or alkyl phosphoric acid esters in an organic solvent and coating it.
However, the thus-obtained thin metal film type magnetic recording medium is not satisfactory and further improvements are still required, because, the running properties and wear resistance are not sufficient, and electromagnetic properties are deteriorated because of spacing loss between a magnetic head and a tape due to the thickness of a protective or lubricating layer.